Difficulty seeing up close
Having difficulty seeing things up close is something that everybody will likely experience at some point in life.
Symptoms of farsightedness can include difficulty seeing clearly for up-close tasks such as reading and computer use. In many cases, the eye compensates this defective near vision with increased muscular effort. While the visual cause of the problem may remain undetected, it ends up revealing itself through headaches, tiredness or neck and back pain. If you suffer from such symptoms, you should see an eye care professional.
There are two main possible causes that result in difficulties seeing up close:
Hyperopia is what happens when the eye is too short versus the refractive power of the crystalline lens. Focusing then takes place behind the retina, instead of directly on it. This causes the retinal image to be blurred, like a photo taken by an unfocused camera lens.
The most common case is when the autofocus mechanism of the eye is defective. This happens to most people by the time they reach their mid-forties. Because the mid-forties used to be considered old age, this condition is called presbyopia in English. Other languages, for instance Portuguese, prefer to use the softer expression “tired vision.”
The simple solution for near-vision difficulties is to wear glasses with lenses that allow the light to focus directly onto the retina again. Lenses that correct near vision are sometimes called “positive lenses” because they bring forward the position of light focusing.
People suffering from hyperopia generally use a lens that is positive on the entire lens surface. Their eye being too short causes eye fatigue when looking at far away objects.
On the contrary, people with a defective or tired autofocus system preferably use a lens with a positive part only in the bottom of the lens. The positive power, called addition, kicks in only when needed to replace the disabled focusing system of the eye, and doesn’t disturb the quality of vision at far distances.
These lenses, called progressive addition lenses, involve complex optical surfaces and are crafted to excellence by Nikon.